1. Field of the Invention
The present invention relates to a method and a device for obtaining calibration data used to display loads of a mechanical press, and it concerns a device for calculating loads of the mechanical press based on the obtained calibration data and displaying the calculated values.
2. Explanation of Earlier Technology
A working operation of a mechanical press prefers precisely measuring loads during a press working so as to determine adequate working conditions. In order to measure the loads, a conventional technique has adhered a strain gauge to a pressure receiving structural portion such as a frame and a connecting rod of the mechanical press and has detected strain of the pressure receiving structural portion. Then it has converted the detected strain to loads.
However, since the measured values of the strain vary depending on the positions where the strain gauge is adhered, the conventional technique had to search a proper position for adhering the strain gauge and calibrate the measured values. This made it troublesome to measure loads of a mechanical press and besides caused a large measurement error.
In order to solve the problems, the present inventor proposed a method for measuring loads by utilizing an overload absorbing hydraulic chamber provided in the mechanical press (see Japanese Patent Appln. No. 11-121756), prior to the present invention.
The earlier proposal preliminarily inputs to a microcomputer, corresponding relationships between loads of the mechanical press and oil pressures of the hydraulic chamber as load displaying calibration data. It detects maximum oil pressure of the hydraulic chamber when conducting a press working and measures loads during the press working based on the maximum oil pressure and the calibration data.
In order to obtain the calibration data, a below-mentioned method is considered.
The method comprises actually imposing on a mechanical press a large number of loads extending from no load to maximum load and measuring a largeness of each load by a load cell, a measuring hydraulic cylinder or the like as well as a peak pressure of the hydraulic chamber when each load is imposed, to thereby obtain relative relationships between the loads and the oil pressures.
However, the above-mentioned method has to prepare a special load measuring instrument such as the load cell and the measuring hydraulic cylinder and besides requires high expertise and long experience for handling such a load measuring instrument. Additionally, it needs to subject the measured data to a troublesome calibration work. Therefore, it takes lots of labor to obtain calibration data peculiar to every mechanical press. On this point this method still had to be improved.
The present invention has a first object to provide a method which makes it possible to easily obtain calibration data peculiar to every mechanical press. It has a second object to provide a device which makes it possible to readily obtain the calibration data. Further, it has a third object to provide a device which can display loads of a mechanical press based on the obtained calibration data with a high accuracy.
In order to accomplish the first object, an invention of claim 1 has constructed a method for obtaining calibration data of a mechanical press in the following manner, for example, as shown in FIGS. 1 to 3 as well as in FIGS. 4(A) and 4(B).
The method obtains load displaying calibration data by utilizing the fact that a load (F) of the mechanical press 1 is proportional to strain of the mechanical press 1 and a die height (H) set through a die height adjusting mechanism 20.
It comprises the steps of:
seeking at least two reference die height positions (a)(f) where the load (F) comes to a small load value (Fa) and a large load value (Ff);
selecting intermediate die height positions (b,c,d,e) corresponding to a plurality of intervening load values (Fb,Fc,Fd,Fe) between the small load value (Fa) and the large load value (Ff);
sensing values (Pa,Pb,Pc,Pd,Pe,Pf) correlative to strain and corresponding to the respective die height positions (a,b,c,d,e,f) by imposing a load on the mechanical press 1 at each of the die height positions (a,b,c,d,e,f); and
obtaining relative relationships between the load values (Fa,Fb,Fc,Fd,Fe,Ff) corresponding to the plurality of die height positions (a,b,c,d,e,f) and the sensed values correlative to strain (Pa,Pb,Pc,Pd,Pe,Pf) as load displaying calibration data (FP).
The invention of claim 1 functions in the following manner, for example, as shown in FIGS. 1 to 3 as well as in FIGS. 4(A) and 4(B).
When obtaining calibration data corresponding to a characteristic curve (B) in FIG. 4(B), first, the die height adjusting mechanism 20 is adjusted to impose a load (F) on the mechanical press 1. Then it seeks a reference die height position (a) where the load (F) comes to a small load value (here minimum load value) (Fa) as well as a reference die height position (f) where the load (F) comes to a large load value (here maximum load value) (Ff).
Next, it selects a plurality of intermediate die height positions (b . . . e) at a predetermined interval between the reference die height positions (a) and (f). In this case, as shown by a straight line (A) in FIG. 4(A), owing to the fact that the load (F) of the mechanical press 1 is proportional to the die height (H) set through the die height adjusting mechanism 20, a plurality of intervening load values (Fb . . . Fe) between the small load value (Fa) and the large load value (Ff) also linearly correspond to the selected intermediate die height positions (b . . . e). Therefore, the intervening load values (Fb . . . Fe) can be calculated based on the intermediate die height positions (b . . . e) and the straight line (A). This dispenses with a necessity of actually measuring them.
Subsequently, through a sensing means 33, it senses values (Pa . . . Pf) correlative to strain (here oil pressures) and corresponding to the respective die height positions (a . . . f) by imposing a load on the mechanical press 1 at each of the die height positions (a . . . f). Then it obtains relative relationships between the load values (Fa . . . Ff) corresponding to the die height positions (a . . . f) and the sensed values correlative to strain (Pa . . . Pf) as the characteristic curve (B) (calibration data (FP)).
As mentioned above, the invention of claim 1 does not have to use any special load measuring instrument such as the load cell and the measuring hydraulic cylinder when obtaining the calibration data. This dispenses with not only high expertise and long experience but also the troublesome calibration work.
Further, the intervening load values between the small load value and the large load value can be calculated based on the fact that they linearly correspond to the intermediate die height positions and need not be actually measured. This can remove the measuring work of the intervening load values.
In consequence, it can readily obtain calibration data peculiar to every mechanical press.
An invention of claim 2, in the invention as set forth in claim 1, imposes a load on the mechanical press 1 at each of the die height positions (a,b,c,d,e,f) and senses a peak oil pressure of an overload absorbing hydraulic chamber 13 provided in the mechanical press 1 by an oil pressure sensing means 33. It takes the thus sensed peak oil pressures (Pa,Pb,Pc,Pd,Pe,Pf) as the value correlative to strain.
The invention of claim 2 can obtain the calibration data by utilizing the overload absorbing hydraulic chamber provided in the mechanical press and therefore need not provide a device dedicated for obtaining the calibration data anew. In consequence, it can obtain the calibration data easily with a simple construction.
In order to seek the reference die height positions (a)(f), an invention of claim 3, in the invention as set forth in claim 2, preliminarily acquires values of reference peak oil pressures (Pa)(Pf) corresponding to the small load value (Fa) and the large load value (Ff), and it takes die height positions when the oil pressure sensing means 33 has sensed the reference peak oil pressures (Pa)(Pf) with loads imposed on the mechanical press 1, as the reference die height positions (a)(f).
The invention of claim 3 can seek two reference die height positions by using the oil pressure sensing means of the overload absorbing hydraulic chamber provided in the mechanical press. Therefore, it can easily seek these positions with a simple construction.
In order to accomplish the second object, an invention of claim 4 has constructed a device for obtaining calibration data of a mechanical press in the following manner, for example, as shown in FIGS. 1 to 3 as well as in FIGS. 4(A) and 4(B).
The device obtains load displaying calibration data by utilizing the fact that a load (F) of the mechanical press 1 is proportional to strain of the mechanical press 1 and a die height (H) set through a die height adjusting mechanism 20. Further, at least two reference die height positions (a)(f) where the load (F) comes to a small load value (Fa) and a large load value (Ff) are sought, and intermediate die height positions (b,c,d,e) corresponding to a plurality of intervening load values (Fb,Fc,Fd,Fe) between the small load value (Fa) and the large load value (Ff) are selected.
The device comprises a sensing means 33 which senses values (Pa,Pb,Pc,Pd,Pe,Pf) correlative to strain and corresponding to the plurality of die height positions (a,b,c,d,e,f), a data inputting means 31, and a calibration data storing means 40.
The calibration data storing means 40 stores relative relationships between the load values (Fa,Fb,Fc,Fd,Fe,Ff) corresponding to the die height positions (a,b,c,d,e,f) and the sensed values correlative to strain (Pa,Pb,Pc,Pd,Pe,Pf) as the load displaying calibration data (FP).
The invention of claim 4 embodies the method for obtaining calibration data as set forth in claim 1 and presents substantially the same function and effect as those of claim 1.
More specifically, it does not have to use any special load measuring instrument such as the load cell and the measuring hydraulic cylinder when obtaining the calibration data. This dispenses with not only high expertise and long experience but also the troublesome calibration work.
Besides, the plurality of intervening load values between the small load value and the large load value can be calculated based on the fact that they linearly correspond to the intermediate die height positions and need not be actually measured. This can remove the measuring work of these intervening load values.
In consequence, it can readily obtain calibration data peculiar to every mechanical press.
An invention of claim 5, in the invention as set forth in claim 4, imposes a load on the mechanical press 1 at each of the die height positions (a,b,c,d,e,f) and senses a peak oil pressure of an overload absorbing hydraulic chamber 13 provided in the mechanical press 1 by the sensing means 33. It takes the thus sensed peak oil pressures (Pa,Pb,Pc,Pd,Pe,Pf) as the values correlative to strain.
The invention of claim 5 can obtain the calibration data by utilizing the overload absorbing hydraulic chamber provided in the mechanical press. This dispenses with a necessity of providing a device dedicated for obtaining the calibration data anew. In consequence, it can easily obtain the calibration data with a simple structure.
In order to accomplish the third object, an invention of claim 6 has constructed a device for displaying loads of a mechanical press in the following manner, for example, as shown in FIGS. 1 to 3 as well as in FIGS. 4(A) and 4(B).
It comprises an overload absorbing hydraulic chamber 13 provided within a slide 4 of the mechanical press 1 and a die height adjusting mechanism 20 arranged in the slide 4, an oil pressure sensing means 33 being connected to the hydraulic chamber 13.
By utilizing the fact that a load (F) of the mechanical press 1 is proportional to a pressure (P) of the hydraulic chamber 13 and a die height (H) set through the die height adjusting mechanism 20, it obtains a relative relationship between the load (F) and the pressure (P) of the hydraulic chamber 13 as load displaying calibration data (FP) and preliminarily inputs the calibration data (FP) to a calculating device 35.
Based on maximum oil pressure (PMAX) sensed by the oil pressure sensing means 33 during a press working and the calibration data (FP), the calculating device 35 calculates the load (F) of the mechanical press 1 and the calculated load (F) is displayed by a display 36.
The calculating device 35 comprises a calibration data storing means 40 which stores the calibration data (FP), storing means 44,45 which store minimum oil pressure (PMIN) sensed by the oil pressure sensing means 33 and the maximum oil pressure (PMAX), respectively, a program command means 46 which commands a correcting calculation and a load calculation according to predetermined procedures, a preload pressure comparing means 47 which monitors variation of the minimum oil pressure (PMIN), a correcting means 48 which corrects the calibration data (FP) in accordance with the variation, and a calculating means 49 which calculates the load (F) from the corrected calibration data (FP) and the maximum oil pressure (PMAX).
The invention of claim 6 corrects the calibration data in accordance with the variation of the minimum oil pressure within the hydraulic chamber. Therefore, it can precisely calculate an actual load during a press working by resorting to the corrected calibration data, which results in the possibility of displaying the actual load during the press working with a high accuracy.